The present invention relates to a fire extinguishing composition. More particularly, the present invention relates to a dry fire extinguishing composition particularly useful in extinguishing Class B fires.
Fire extinguishers and fire extinguishing compositions, in general, are designed for extinguishing incipient fires. Incipient fires are divided into three general groups; namely, Class A, Class B and Class C. Class A fires are those occurring in ordinary combustible material, where the quenching and cooling effects of quantities of water or solutions containing a large percentage of water are of primary importance. This, of course, is the least difficult type of fire to extinguish. Class B fires are those occurring in oils, greases, flammable liquids, etc., where the blanketing or smothering effect of the extinguishing agent is of greatest importance. In this type of fire, liquid extinguishing materials are generally useless, particularly since they cause splattering, etc. of the liquid material which is aflame. Fires of this type are also the most difficult to extinguish since it is also necessary that the heat be cut off after the fire is initially extinguished so that the fire will not flashback or reignite in the liquid material. Hence, a fire extinguishing material for this type of fire must not only extinguish the original flame in a very short time but must have a holding capacity to maintain this condition and prevent or abate flashback or reignition. Class C fires are incipient fires of electrical equipment, where the non-conducting property of the extinguishing material is of prime importance. In this particular case, dry fire extinguishing agents are also more useful than liquid types not only because of their nonconductive properties but also because of their ability to abate reignition. In short, generally the same types of fire extinguishing materials as are useful for Class B fires are also best for Class C fires because of the possibility of reignition until the condition causing the fire has been remedied.
Statistics show that approximately 14 percent of all home fires are the result of Class B fires on kitchen ranges. Such fires are also quite prevalent on cooking units in restaurants, ship galleys, cooking units in recreational vehicles, etc. Under these conditions, one is not only faced with the inherent problems of Class B fires but the idiosyncrasies of use involved. As previously mentioned, there is the problem of the extinguishing agent causing the flaming oil or other liquid to splatter and thus spread the fire. It is also necessary, under these circumstances, that the fire be extinguished in an extremely short period of time, particularly where a vented hood is utilized above the cooking unit. Where a vented hood is utilized over the cooking unit, there is a tendency for grease and oil to accumulate in the fan and vent and any flame on the surface of the cooking unit will rapidly pass to the vent and ignite the collected oils and greases. Also, in connection with Class B fires and cooking units, in most cases the fire starts while the cooking unit is unattended, and, therefore, the heat under the cooking utensil or other item will not be turned off immediately. Consequently, even though the fire is initially extinguished, the heat under the oil or grease in the cooking utensil will flashback or reignite. One suggested solution to this problem has been to provide elaborate automatic cutoff systems for the burners of the cooking unit. However, this is, at best, an expensive and unsatisfactory solution. Accordingly, the most simple and inexpensive solution would be to provide a fire extinguishing material which would not only initially extinguish the flame in a very short time but would also hold this condition for an extended period of time even though the heat on the burner is not cut off. Finally, there is the problem of locating a fire extinguisher in the vicinity of the cooking unit so that it can be automatically triggered and extinguish the fire on the cooking unit. To date, this has been virtually impossible because of the lack of suitable extinguishing materials which are capable of withstanding the high temperatures and moisture conditions associated with normal cooking over an extended period of time. To date, there has been no satisfactory solution to this problem, since most known fire extinguishing compositions deteriorate over a period of time and must be replaced or renewed, and the problem is exaggerated by the heat and moisture to which the material would be subjected during normal cooking operations.
A large number of conventional fire extinguishers are charged with liquid type fire extinguishing materials. Obviously, Class B fires cannot be extinguished with water because of the extreme danger of splattering caused by the water hitting the flaming oil or grease. The same applies to any extinguishing composition containing substantial amounts of water, such as, calcium chloride solution. Consequently, carbon tetrachloride is one of the few known liquid extinguishing materials which is useful for extinguishing Class B and Class C fires. Carbon tetrachloride also has the advantage, over calcium chloride solutions and the conventional foam-type extinguishing materials, that it need not be renewed on a yearly basis as do the latter. While materials, such as, percloroethylene, bromocloroethane and methylbromide, have certain advantages over the previously mentioned liquid or foam-type extinguishing materials, these materials are rather expensive compared with the more common types of extinguishing agents. Most importantly, all known liquid type fire extinguishing materials have boiling points below about 121.degree. C. and therefore, these materials cannot be depended upon to last for any significant length of time when subjected to conventional temperatures encountered above a cooking range. While percloroethylene does have a boiling point of 121.degree. C., all of the other liquids or solutions mentioned have boiling points below about 100.degree. C. Thus, the materials will evaporate quite rapidly under normal cooking range conditions, and there is no guarantee that sufficient material will remain unevaporated when the need arises. Consequently, extinguishing materials for Class B fires, particularly on cooking ranges, are preferably the dry type fire extinguishing materials.
Most of the more common dry type fire extinguishing materials are useful in both Class B and Class C fires. This is due to the fact that these finely divided powders or dusts generally do not cause splattering of the flaming oil or grease. While potassium aluminum flouride and mono- and di-ammonium phosphates have certain advantages over the more common types of dry chemical fire extinguishers, these materials are substantially more expensive. Therefore, the ideal and most effective materials in this category are the alkali metal bicarbonates and the alkaline earth metal carbonates, such as, sodium and potassium bicarbonates and calcium carbonate. The alkaline earth metal carbonates and alkali metal bicarbonates release carbon dioxide when the extinguishing material is heated by the flame of the ignited material. This carbon dioxide is, of course, heavier than air and blankets the flaming material, thus preventing access to ambient air. One drawback of dry type fire extinguishing agents is their tendency to cake or agglomerate when subjected to moisture, even of the atmosphere, over long periods of time. Consequently, the free flowing character of the material is reduced so that it may be difficult to expel from the extinguisher when needed. This problem, however, has been satisfactorily solved by the addition to the dry chemical extinguishing agent of very small amounts of dissicants; for example, magnesium stearate, talc, silica, silica gel, diatomaceous earth, calcium chloride, etc. While the dry chemical fire extinguishing agents previously mentioned, particularly the carbonates and bicarbonates, are quite effective in initially extinguishing Class B type fires, it has been found that these materials alone lack the capacity to hold the extinguished condition and prevent or abate flashback or reignition. As previously mentioned, such flashback or reignition generally follows if the heat is not cut off beneath the cooking utensil or the like item containing the grease or oil.
Finally, in both liquid and dry extinguishing materials, there are those which release toxic gases or leave toxic residues.
It is therefore an object of the present invention to provide a solution to the above-mentioned problems of the prior art fire extinguishing compositions. Another and further object of the present invention is to provide an improved dry fire extinguishing composition. Yet another object of the present invention is to provide an improved dry fire extinguishing composition which is particularly useful in extinguishing Class B fires. Still another object of the present invention is to provide an improved dry fire extinguishing composition which is particularly useful in extinguishing Class B fires on cooking units. A further object of the present invention is to provide an improved dry fire extinguishing composition which is relatively inexpensive. Another object of the present invention is to provide an improved dry fire extinguishing composition which is non-toxic and has no serious after effects when utilized for extinguishing fires on cooking units. A still further object of the present invention is to provide an improved dry fire extinguishing composition which is capable of rapidly extinguishing a Class B fire. Another object of the present invention is to provide an improved dry fire extinguishing composition which is highly effective in preventing or abating flashback or reignition after the fire has been initially extinguished. Another and further object of the present invention is to provide an improved dry chemical fire extinguishing material which is highly effective in rapidly extinguishing the initial flame and is also highly effective in preventing or abating flashback or reignition even though the heat adjacent the ignited material is not reduced. Yet another object of the present invention is to provide an improved dry fire extinguishing composition which is capable of withstanding varying temperatures and conditions of high humidity over extended periods of time without deterioration. These and other objects and advantages of the present invention will be apparent from the following detailed description.